I have upgraded from BT full fibre 100 with Halo 3 to full fibre 500 with halo 3 on august 20th of august. It was implied that it would be active as of 22nd of august. A month on I am still waiting for any sort of feedback as to whether my upgrade is going to be activated, I have an email with an acknowledgement of my order and an update in my contract.
have you phone CS 03301234150 and see if they can help you
what does your package say you have in MYBT?